Battle of Iwate Fields

The Battle of Iwate Fields (1545) was the first battle of Harumune Date's campaigns during the Sengoku Jidai and the decisive battle of the Tenbun War. Harumune Date defeated and deposed his father Tanemune Date after routing his smaller rebel army in Mutsu Province.

Background
In 1542, the Date clan daimyo Tanemune Date alienated his son Sanemoto Date by planning to marry him to an Uesugi princess so that he would become the leader of the Uesugi clan, so Harumune Date stood by his younger brother and led a rebellion, starting the "Tenbun War" of 1542-1548. By 1545, Tanemune had 465 troops to face his son's 570 troops, who had taken over Mutsu Province. Now, it appeared as if the father Tanemune was actually the rebel. Harumune led his army against his father at Iwate Fields during the spring, preparing for the decisive battle of the war.

Battle
Harumune had a numerically-superior army, and he was forced to go on the attack when his father's army took up position on a hillside. Harumune led his troops in a charge against his father, whose Yari Ashigaru were initially hidden. However, the Date discovered them during the charge, and the Date clan fought against the rebels in bloody melee. The numerically-superior Date forces proved their power by massacring the rebels in battle, and Tanemune's rebellion was crushed at the battle.

Aftermath
The victory at Iwate Fields consolidated the might of the Date clan under Harumune while Tanemune, deposed, lived until 1565 under his sons' rule. The Mogami clan, which declared its independence from the Date during their civil strife, were next on the list of enemies that the Date had to deal with, and by 1550 the Date were firmly established as the dominant power in northern Honshu after conquering the Mogami as well as annexing the Hatakeyama clan's Miyagi Prefecture.